A major waste management problem involves disposal of sewage sludge. The problems concerning disposal of sewage sludge have existed for a considerable period of time. Attempts to remove the water from sewage sludge have not been especially satisfactory. For instance, it is extremely difficult to reduce the water content of sewage sludge below about 85%, such as by mechanical methods such as centrifuges, belt presses and screens. Moreover, methods that employ evaporation by heating have not been particularly attractive from a commercial viewpoint, because of the relatively large energy requirements.